orb@whuts.UUCP (SEVENER) (09/03/86)
Yet another item in the news recently of relevance to the problem
of the safe supply of energy. The New York Times a month ago
reported on an experiment with geothermal energy in Maryland in
which a hole was dug deep enough to hit the hot rocks underneath
the surface. It successfully produced electricity.
The major advance of the technique is that unlike other geothermal
techniques which rely on natural geysers or other such sources of
steam, this technique could essentially be used practically anywhere.
It just means digging deep enough to reach the region of the
earth's crust beneath the surface which is constantly hot.
The report said that such a hole could produce energy for a period
of some years. Then it would just be a few thousand years for the
heated rock to regain its heat from the earth's core.
An intriguing possibility...
Of course one would want to consider effects of geological stability.
tim sevener whuxn!orjmc@riccb.UUCP (Jeff McQuinn ) (09/05/86)
> The major advance of the technique is that unlike other geothermal > techniques which rely on natural geysers or other such sources of > steam, this technique could essentially be used practically anywhere. > It just means digging deep enough to reach the region of the > earth's crust beneath the surface which is constantly hot. > The report said that such a hole could produce energy for a period > of some years. Then it would just be a few thousand years for the > heated rock to regain its heat from the earth's core. > > An intriguing possibility... > Of course one would want to consider effects of geological stability. > tim sevener whuxn!or I saw a program on Nova or one of the Chicago City College courses on T.V. that covered this very topic. As I recall it's not just a matter of plunking down a hole any old place and getting free energy. Like other energy sources, the energy itself is free but you pay to get it from where it found to where it is needed and in converting it from it's present form to what you can use. The main problem with geothermal wells is that you tend to have to dig VERY deep wells. Few places exist where magma is close enough to the surface to heat groundwater. If an injection well is used it would be assumed that vast quantities of water need to be available. The biggest problem is that the heated water picks up so many minerals that it is essentially polluted. If surface water is injected into a dry well to pick up heat you cannot just dump it after removing the heat or you'll end up creating a salt bed. The same water could be used in a closed system but this implies that you'll have to plant a large heat exchanger at the bottom of the well. That's an enormously expensive proposition. If the well is tapping a ground water source the water can be reinjected at another location. Eventually the reinjected water poisons the main well and not enough hot water is drawn to make it worth the effort. The hot ground water is also heavily laden with minerals and tends to be corrosive and very hard on the equipment. The temperature of the water was not high enough to efficiently create electricity (in the program) but was suitable for heating houses in a small city. But the cost of the pumping station and two wells (main well and reinjection well) over the useful lifetime of the wells was not competative with natural gas. Jeff McQuinn jes' VAXing around
bob@islenet.UUCP (Bob Cunningham) (09/11/86)
> The main problem with geothermal wells is that you tend to have to dig > VERY deep wells. Few places exist where magma is close enough to the > surface to heat groundwater... It's surprising how many places are suitable: portions of the U.S. Pacific northwest, California, Japan, etc. along the "ring of fire" circling the Pacific Ocean, plus the Hawaiian islands (where there is very active development of geothermal sources). Not so surprisingly (given the geological conditions) those are precisely areas where coal generally isn't. The temperature difference doesn't have to be extreme, remember that ocean thermal energy conversion technology works with a relatively small thermal difference (though it does require lots of water, and thus its usefulness is primarily confined to ocean & nearshore sites between 35 degrees north or south of the Equator). -- Bob Cunningham {humu|ihnp4}!{islenet|uhmanoa}!bob cunninghamr%haw.sdscnet@LLL-MFE.ARPA Hawaii Institute of Geophysics, University of Hawaii